Paper finds "Evaporation of water causes global cooling, not warming"

A tweet today from Dr. Ken Caldeira references a paper he co-authored published in Environmental Science Letters about 3 years ago which finds that increased evaporation of water leads to global evaporative cooling, not global warming. Thus, increased evaporation of water vapor from warming would be a negative feedback, not positive as commonly assumed. 

Catastrophic climate alarmism is based upon the assumption that water vapor feedback is positive and amplifies a small warming from CO2 by a factor of 3-5 times to produce a climate catastrophe. If, as this paper and several others find, water vapor feedback is instead negative, the climate sensitivity or warming from increased CO2 after feedbacks drops to insignificant, negligible levels and the climate catastrophe would effectively be called off.

According to Dr. Caldiera's paper,

Increased latent heat flux to the atmosphere has a local cooling influence known as 'evaporative cooling', but this energy will be released back to the atmosphere wherever the water condenses [added: which is usually in the upper troposphere]. However, the extent to which local evaporative cooling provides a global cooling influence has not been well characterized. 

We find that globally adding a uniform 1  W m − 2 source of latent heat flux along with a uniform 1  W m − 2 sink of sensible heat leads to a decrease in global mean surface air temperature of 0.54 ± 0.04 K. This occurs largely as a consequence of planetary albedo increases associated with an increase in low elevation cloudiness caused by increased evaporation. Thus, our model results indicate that, on average, when latent heating replaces sensible heating, global, and not merely local, surface temperatures decrease.

The IPCC alleges 1 Wm-2 increase in radiative forcing causes a 3C/3.7 Wm-2 or .81C increase in surface temperature, but if evaporative cooling from water vapor offsets this by 66% or 0.54C according to Dr. Caliera's paper, only a 0.27C residual warming would remain. Therefore, climate sensitivity to a doubling of CO2 levels after evaporative cooling from water vapor would only be ~.33*3C = 1C, i.e. not of concern and likely beneficial.

Tweet today from Dr. Caldeira in reply to another climate scientist (who just published a paper claiming evaporation of water causes global warming) notes that "evaporation of water causes global cooling in the NCAR [the US National Center for Atmospheric Research] atmospheric model, not warming"  

Ken Caldeira‏@KenCaldeira

.@mzjacobson Evaporation of water causes global cooling in the NCAR atmospheric model, not warming. http://iopscience.iop.org/1748-9326/6/3/034032/ … @mike_cal

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11:46 AM - 2 Aug 2014

Environmental Research Letters Volume 6 Number 3

George A Ban-Weiss et al 2011 Environ. Res. Lett. 6 034032 doi:10.1088/1748-9326/6/3/034032

Climate forcing and response to idealized changes in surface latent and sensible heat

FEATURED ARTICLE

George A Ban-Weiss1,3, Govindasamy Bala2, Long Cao1, Julia Pongratz1 and Ken Caldeira1

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AbstractReferencesCited BySupplementary DataMetrics

Land use and land cover changes affect the partitioning of latent and sensible heat, which impacts the broader climate system. Increased latent heat flux to the atmosphere has a local cooling influence known as 'evaporative cooling', but this energy will be released back to the atmosphere wherever the water condenses. However, the extent to which local evaporative cooling provides a global cooling influence has not been well characterized. Here, we perform a highly idealized set of climate model simulations aimed at understanding the effects that changes in the balance between surface sensible and latent heating have on the global climate system. We find that globally adding a uniform 1  W m − 2 source of latent heat flux along with a uniform 1  W m − 2 sink of sensible heat leads to a decrease in global mean surface air temperature of 0.54 ± 0.04 K. This occurs largely as a consequence of planetary albedo increases associated with an increase in low elevation cloudiness caused by increased evaporation. Thus, our model results indicate that, on average, when latent heating replaces sensible heating, global, and not merely local, surface temperatures decrease.